Compositions and methods for improving cold tolerance in animals and humans

ABSTRACT

The invention disclosed is a composition for improving cold tolerance in animals and humans, comprising an adenosine receptor antagonist or an adenosine de-activator. Preferably, a nutritional supplement is also provided which further enhances cold tolerance. The nutritional supplement includes various combinations and amounts of carbohydrate, protein and fat.

This is a continuation of application Ser. No. 07/287,974, filed Dec. 12, 1988, now abandoned.

This invention relates to improving cold tolerance and prevention of accidental hypothermia in animals and humans.

When exposed to severe cold, mammals increase their heat production to counter heat loss in order to maintain a constant body temperature. If heat loss surpasses maximum heat production, hypothermia results and unless aided by exogenous heat, death ensues. Given that defence operations and emergencies can involve prolonged cold exposure, any treatment that may enhance thermogenesis would be beneficial in reducing or eliminating the danger of becoming hypothermic.

Theophylline (THEO) and aminophylline (AMPY; 85% theophylline, 15% ethylenediamine) have been shown to elevate maximum thermogenesis and to improve cold tolerance in animals and man in severe cold. However, their mechanism of action is widely disputed. One school of thought is that competitive inhibition of phosphodiesterase (PDE) activity and thus increased levels of intracelleular cAMP for enhanced substrate conversion and mobilization is responsible. Another involves competitive antagonism against adenosine receptors, thereby releasing the antilipolytic effect of adenosine after sympathetic stimulation in the cold. Since both of these known compounds are non-selective adenosine antagonists, i.e. they exhibit other pharmacological activity, the operating mechanism was uncertain.

In considering the possible role of adenosine in thermogenesis, adenosine is formed as an end product of ATP hydrolysis following physiological stimulation, e.g. adrenergic or local hypoxia. It is released into extracellular space and binds to adenosine receptors on the cell surface and exerts an inhibiting influence on substrate (fuel) mobilization. Since substrate availability is a critical limiting factor for full expression of heat producing capability in the cell, a shortage of fuel supply would lend to less than full expression of thermogenic capability and reduced cold resistance. The use of adenosine antagonists should rectify this deficiency and amplify the body's own cold fighting ability.

To test the mechanism of adenosine antagonism, a known selective adenosine receptor antagonist, 8-phenyltheophylline (8-PT) which preferentially binds to adenosine receptors was used. To test the mechanism of PDE inhibition, a selective PDE inhibitor, enprofylline (ENPRO) which is devoid of adenosine antagonism was employed.

It was also contemplated that if adenosine antagonism was established as the operating mechanism, other means for blocking the effects of adenosine could achieve the same result. Accordingly, adenosine de-activators were employed.

It was found by applicant that rats receiving ENPRO (1.5 and 15 mg/kg, i.p.) failed to show enhanced thermogenesis. In contrast, treatment with either enzyme de-activator or optimal doses of 8-PT significantly increased (p<0.05) thermogenesis and cold tolerance.

Having established that the operating mechanism for improved thermogenesis and cold tolerance clearly involves the competitive antagonism against adenosine receptors, according to the invention, a method for improving the cold tolerance of animals and humans is contemplated, which comprises ingesting orally or injecting into an animal or human host (a) a therapeutically effective amount of an adenosine receptor antagonist, excluding theophylline and aminophylline alone; or (b) an adenosine de-activator.

Representative adenosine receptor antagonists include xanthines of the structural formula ##STR1## wherein R₁ and R₂ are H or C₁₋₄ lower-alkyl, R₄ is H or CH₃, and ##STR2## H; provided that when R₁ and R₂ are both CH₃, R₃ and R₄ are not both H.

Other non-xanthine adenosine antagonists such as triazoloquinazoline, pyrazoloquinoline, pyrazolopyridine and imidazopyrimidine are also contemplated.

In the drawing which illustrates the preferred embodiments of the invention:

FIG. 1 is a graph which illustrates the effect of injected 8-phenyltheophylline (8-PT) on heat production;

FIG. 2 is a graph which illustrates the effect of injected 8-cyclopentyltheophylline (CPT) on heat production;

FIG. 3 is a graph which illustrates the effect of injected caffeine on heat production;

FIG. 4 is a graph which illustrates the effect of injected theobromine on heat production.

FIG. 5 is a graph which illustrates the effect of orally administered theobromine (in the form of cocoa) on heat production.

FIG. 6 is a graph which illustrates the effect of injected 8-(4-(2-aminoethyl)amino) carboxylmethyloxyphenyl)-1,3-diproplyxanthine (XAC) on heat production;

FIG. 7 is a graph which illustrates the effect of injected 8-(2-amino-4-chlorophenyl)-1,3-dipropyl xanthine (PACPX) on heat production;

FIG. 8 is a graph which illustrates the effect of injected 8-(p-sulfophenyl)-1,3-dipropyl xanthine (DPSPX) on heat production;

FIG. 9 is a graph illustrating the effect of enprofylline (ENPRO) on heat production;

FIG. 10 is graph which illustrates the effect of combined 8-PT and AMPY administration on heat production;

FIG. 11 is a graph which illustrates the effect of adenosine deaminase on heat production;

FIG. 12 is a graph which illustrates the effects of placebo treatments, nutritional supplement alone, and theobromine (4 mg/kg p.o.) plus nutritional supplement on cold tolerance in a female subject; experimental protocol as in Table 4;

FIG. 13, is a graph which illustrates the effect of theobromine (4 mg/kg p.o.) and nutritional supplement on improving cold tolerance in a male subject; experimental protocol as in Table 4;

FIG. 14 is a graph which illustrates the benefit of a combination theobromine (4 mg/kg p.o.) and nutritional supplement on improving cold tolerance in humans (3 males, 2 females); experiment protocols as in Table 4;

FIG. 15 is a graph which illustrates the effects of placebo treatments and theobromine (2 mg/kg p.o.) plus nutritional supplement on cold tolerance in two male subjects; experimental protocol as in Table 5; and

FIG. 16 is a graph which illustrates the effects of placebo treatments and theobromine (in the form of cocoa powder containing 1.5% theobromine for an equivalent 2 mg/kg p.o.) plus nutritional supplement on cold tolerance in two subjects (one male, one female); experimental protocol as in Table 6.

EXPERIMENTAL

The following additional pure chemical compounds which are known to have adenosine antagonistic effects were tested for increased heat producing capability and hence improved cold tolerance in animals and humans:

8-cyclopentyltheophylline (CPT);

8-phenyltheophylline (8-PT);

8-(4-(2-aminoethyl)amino) carboxylmethyloxyphenyl)-1,3-dipropylxanthine (XAC);

8-(2-amino-4-chlorophenyl)-1,3-dipropylxanthine (PACPX);

8-(p-sulfophenyl)-1,3-dipropyl xanthine (DPSPX);

caffeine (1,3,7-trimethylxanthine); and

theobromine (3,7-dimethylxanthine).

CPT has the advantage of being highly soluble in water and is thus the easiest to administer by injection.

Caffeine is also easily soluble in water but its adenosine antagonistic effect is not as strong as that of CPT. Theobromine is not very soluble in water; we circumvented this problem by applying both injection and oral administration. The other compounds are dissolved in suitable organic solvents, i.e. in polyethylene glycol (8-PT) or DMSO (XAC, PACPX and DPSPX) because of their insolubility in water. Control injections using the vehicle only are required in these cases.

As can be seen from the results, CPT (FIG. 2), PACPX (FIG. 7) and DPSPX (FIG. 8) significantly increased the heat producing capability of the rats and significantly increased their cold resistance as seen by the very much higher final body temperature after 2 hours of severe cold exposure. 8-PT also significantly increased thermogenesis and cold resistance in a dose-dependent manner (FIG. 1). Because of the solubility problem, which presumably affects the absorption of the injected drug following its administration, the dosage difference between the CPT and 8-PT is about 5,000 fold relecting their concentrational differences in in vitro receptor binding studies. Similarly, injection (i.p.) of caffeine at 20 mg/kg (FIG. 3) and theobromine at 20 mg/kg (FIG. 4) also demonstrated significant improvement on thermogenesis and cold resistance in the rats. Interestingly, when theobromine is administered orally to rats (FIG. 5), significant increase in thermogenesis was also observed. Oral theobromine was administered as cocoa powder water. This is because cocoa powder contains about 1-2% of theobromine based on dry weight with little or no other xanthine compounds present as quantified by our HPLC analysis and as indicated in the open literature (e.g. Shively and Tarka, Jr., 1984, In: The Methylxanthine Beverages and Foods: Chemistry, Consumption and Health Effects, edited by G. A. Spiller, New York: Allan Liss, p. 149-178). This indicates that through the oral route, even relatively water insoluble adenosine antagonists, such as theobromine may be quite useful as an agent for the stimulation thermogenesis and improvement of cold resistance. This has been verified in our initial studies in humans (FIGS. 12 to 16).

The results on XAC (FIG. 6) are not as clean-cut as those for the other compounds; the main reason being the solubility problem. However, XAC showed a 7% increase in maximum and total thermogenesis, very close to the 10% or more found in the other compounds which elicited statistically significant increases.

Since some of the xanthines (e.g. caffeine, theobromine) used also possess antiphosphodiesterase enzyme (PDE) activity, it is a possibility that the action of these xanthines may be through PDE inhibition rather than adenosine antagonism. To dispel this possibility, we have selected enprofylline (3-propylxanthine), which is known to have PDE inhibitory effect (IC₅₀ 100-400 μM) but devoid of adenosine antagonism (Persson & Kjellin, Enprofylline, A Principally New Antiasmatic Xanthine, Acta Pharmacol. Toxicol. 49:313-316, 1981) to test its influence on thermogenesis and cold resistance. The results indicated that enprofylline is without effect on stimulation of thermogenesis (FIG. 9), confirming our contention that it is the antagonism of adenosine receptors but not the inhibition of PDE activity that is responsible for the beneficial effects of the many xanthines employed herein. To further demonstrate the validity of this claim, we used an adenosine de-activator which converts adenosine to other metabolizable compounds by chemical means. For example, adenosine deaminase, which converts exclusively adenosine to inosine and thereby eliminates the deleterious effects of adenosine in thermogenesis. As can be seen from FIG. 11, pretreating the rats by injection with adenosine deaminase significantly increased heat production and cold tolerance. It is also contemplated that adenosine kinase, which phosphorylates adenosine to adenosine monophosphate (AMP), would have a similar effect in improving cold tolerance. Optionally, AMP may be further phosphorylated to adenosine diphosphate (ADP) and then to adenosine triphosphate (ATP) by nucleoside monophosphate kinase.

Our results also indicate that the maximum thermogenesis effect by optimal dose of 8-PT (5 mg/kg, i.p.) was significantly lower than that with the optimal dose of AMPY (18.7 mg/kg, i.p.) (FIG. 10). Applicant has found that the deficit could be eradicated by combining optimal 8-PT dose with a low dose of AMPY (1.25 mg/kg, i.p.). In fact, the thermogenic effect of 8-PT, when administered simultaneously with a low dose of AMPY (FIG. 10), is markedly enhanced, and is increased to the same level as that after a high dose of AMPY. As the magnitude of HP induced by the combined drug treatment may have already reached the maximum aerobic capacity of the animal, it is difficult to distinguish whether these two compounds elicit thermogenesis in a synergistic or additive manner.

To demonstrate that a combination of adenosine antagonist and nutritional supplement is a better treatment than the use of adenosine antagonist or nutritional supplement alone, we have conducted experiments in rats verifying this prediction. Tables 1 and 2 below show that orally administered nutritional supplement alone, either in the form of different carbohydrate mixtures or as a mixture of carbohydrates, fat and protein, enhanced heat production and the magnitude and the duration of cold tolerance.

                                      TABLE 1                                      __________________________________________________________________________     EFFECTS OF CARBOHYDRATE                                                        FEEDING ON COLD TOLERANCE IN RATS#                                             Treatment                                                                               Total HP                                                                              Max. HP Change in                                                                               Duration                                      (n-8)    (Kcal) (Kcal/15 min)                                                                          Tb (°C.)                                                                         (min)                                         __________________________________________________________________________     Water 5 ml                                                                              10.90 ± 0.91                                                                       1.50 ± 0.03                                                                         -10.83 ± 0.76                                                                        144.4 ± 6.98                               Sucrose  14.31 ± 1.27*                                                                      1.66 ± 0.04*                                                                         -8.68 ± 0.69                                                                        163.1 ± 7.23*                              52% aq. solution                                                                        (31%)  (10%)                                                          Starch   14.60 ± 0.98*                                                                      1.59 ± 0.05                                                                          -9.05 ± 1.11                                                                        166.9 ± 5.59*                              55.2% aq. solution                                                                      (34%)  (6%)                                                           Gl:Su:St 15.20 ± 0.98*                                                                      1.64 ± 0.05*                                                                         -7.88 ± 0.64*                                                                       172.5 ± 4.59*                              (1:3:6.4)                                                                               (39%)  (9%)                                                           Gl:Su:St 14.41 ± 0.76*                                                                      1.58 ± 0.03                                                                         -10.98 ± 0.89                                                                        170.6 ± 5.89*                              (1:6:3.2)                                                                               (32%)  (5%)                                                           Gl:Su:St 16.63 ± 0.96*                                                                      1.67 ± 0.07*                                                                         -5.50 ± 0.96*                                                                       177.5 ± 2.20*                              (1:5:10.6)                                                                              (53%)  (11%)                                                          Gl:Su:St 15.09 ± 1.78*                                                                      1.68 ± 0.06*                                                                        -10.33 ± 0.97                                                                        170.0 ± 5.38*                              (1:10:5.3)                                                                              (39%)  (11%)                                                          __________________________________________________________________________      #Feeding was by gastric tube in a volume of 5 ml 15 min prior to cold          exposure.                                                                      *Significantly different from water control, p < 0.05 (Wilcoxin's Rank         Test).                                                                         Numbers in brackets indicate percentage increase in heat production over       control value.                                                                 Gl = Glucose; Su = Sucrose; St = Starch                                        The composition of carbohydrate is by weight ratio, wherein 1 = 0.26 g.        The carbohydrate mixtures are dissolved in water.                        

                                      TABLE 2                                      __________________________________________________________________________     EFFECTS OF SUBSTRATE                                                           FEEDING ON COLD TOLERANCE IN RATS#                                             Treatment                                                                            Total HP                                                                              Max. HP Change in                                                                               Duration                                         (n-9) (Kcal) (Kcal/15 min)                                                                          Tb (°C.)                                                                         (min)                                            __________________________________________________________________________     Water 5 ml                                                                           16.12 ± 0.94                                                                       1.67 ± 0.05                                                                         -12.12 ± 0.75                                                                        177.2 ± 8.36                                  Gl:Su:St                                                                             24.61 ± 1.28*                                                                      1.90 ± 0.06*                                                                        -10.42 ± 1.13                                                                        231.7 ± 4.78*                                 (1:5:10.6)                                                                           (53%)  (14%)                                                             Mixture                                                                              25.83 ± 1.64*                                                                      2.01 ± 0.07*                                                                         -8.52 ± 1.83*                                                                       230.0 ± 4.08*                                 (16 Kcal)                                                                            (60%)  (20%)                                                             __________________________________________________________________________      #Feeding was by gastric tube in a volume of 5 ml either 15 min (for            Gl:Su:St) or 30 min (for mixture) prior to cold exposure.                      *Significantly different from water control, p 0.05 (Wilcoxin's Rank           Test). The composition of carbohydrate is by weight ratio.                     Numbers in brackets indicate percentage increase in heat production over       control value.                                                                 Gl = Glucose; Su = Sucrose; St = Starch                                        Composition of mixture = Gl:Su:St:Egg Albumin:Corn Oil1:3:6.4:5:0.33           (weight ratio, wherein 1 =  0.26 g).                                           The mixtures are dissolved in water.                                           Composition of mixture in terms of weight percentages, carbohydrate =          66.2%, fat = 1.9% and protein = 31.9%.                                   

However, as illustrating in Table 3 below, the combination of a general adenosine antagonist, theobromine (administered orally in the form of cocoa powder plus water) and carbohydrate mixtures resulted in the greatest improvement of heat production and cold tolerance as compared to the treatment using water, cocoa, or nutritional supplement alone. Consequently, the decrease of body temperature (Tb) was the least and the duration of cold exposure was the longest in adenosine antagonist and nutritional supplement treatment. It is therefore likely that this combination is the best for improving cold resistance and based on Tables 2 and 3, theobromine plus a nutritional mixture including carbohydrates, protein and fat is a desirable formula.

                                      TABLE 3                                      __________________________________________________________________________     EFFECTS OF COCOA AND CARBOHYDRATE                                              FEEDING ON COLD TOLERANCE IN RATS#                                             Treatment                                                                             Total HP                                                                              Max. HP Change in                                                                               Duration                                        (n-8)  (Kcal) (Kcal/15 min)                                                                          Tb (°C.)                                                                         (min)                                           __________________________________________________________________________     Water 5 ml                                                                            10.75 ± 0.59                                                                       1.42 ± 0.04                                                                         -10.45 ± 0.62                                                                        140.6 ± 5.26                                 Cocoa 1 g                                                                             11.42 ± 0.72                                                                       1.59 ± 0.03*                                                                        -9.84 ± 0.46                                                                         144.4 ± 5.26                                        (6%)   (12%)                                                            Gl:Su:St                                                                              16.04 ± 0.68*                                                                      1.61 ± 0.04*                                                                        -6.85 ± 1.26*                                                                        176.3 ± 3.51*                                (1:3:6.4)                                                                             (49%)  (13%)                                                            Cocoa 1 g +                                                                           17.43 ± 0.64*                                                                      1.72 ± 0.04*                                                                        -5.53 ± 0.87*                                                                        180.0 ± 0.00*                                Gl:Su:St                                                                              (61%)  (21%)                                                            (1:3:6.4)                                                                      Gl:Su:St                                                                              16.49 ± 0.67*                                                                      1.67 ± 0.03                                                                         -5.75 ± 1.12*                                                                        176.3 ± 3.51*                                (1:5.10.6)                                                                            (32%)  (5%)                                                             Cocoa 1 g +                                                                           17.71 ± 0.86*                                                                      1.77 ± 0.10*                                                                        -5.03 ± 1.16*                                                                        180.0 ± 0.00*                                Gl:Su:St                                                                              (65%)  (25%)                                                            (1:5:10.6)                                                                     __________________________________________________________________________      #Feeding was by gastric tube in a volume of 5 ml 15 min prior to cold          exposure. The composition is by weight ratio, wherein 1 = 0.26 g.              *Significantly different from water control, p < 0.05 (Wilcoxin's Rank         Test).                                                                         +Significantly different from cocoa control, p < 0.05 (Wilcoxin's Rank         Test).                                                                         Numbers in brackets indicate percentage increase in heat production over       water control group.                                                           Gl = Glucose; Su = Sucrose; St = Starch                                        The mixtures are dissolved in water.                                     

As seen in Tables 4 to 6 and FIGS. 12 to 16, initial experiments in humans of both sexes have shown that the combination of orally administered theobromine in amounts of 2 to 4 mg/kg of body weight and various combinations of nutritional supplements effective in improving cold tolerance and retarding the onset of hypothermia in severe cold.

With specific reference to FIG. 12, the hatched boxes indicate duration of walking on a motorized treadmill at 4 mile/hr. Arrow indicates time of ingestion of either placebo drink or nutritional supplement. Theobromine is taken orally at time 0.

In FIG. 13, the hatched boxes indicate duration of walking on a motorized treadmill at 5 mile/hr. Arrow indicates time of ingestion of placebo drink and nutritional supplement. Arrows with cocoa on top indicate time of ingestion of cocoa plus nutritional supplement (total amount of theobromine in cocoa and nutritional supplement are equivalent to those in theobromine+nutritional supplement).

In FIG. 14, the hatched boxes indicate duration of walking on a motorized treadmill at 4 or 5 miles/hr (5 for males, 4 for females). Arrow indicates time of ingesting placebo drink or nutritional supplement.

                                      TABLE 4                                      __________________________________________________________________________     Change in rectal temperature (°C.) in male (3) and female (2)           subjects walking (4-5 miles/hour) intermittently (50% of time) at              -10° C. for 3 hours dressed in shorts (males) or T-shirt and            shorts                                                                         (females).                                                                     CHANGE IN RECTAL TEMPERATURE                                                   __________________________________________________________________________     Treatment-Placebo and Placebo                                                  Subjects                                                                       Time                                                                               M.B.                                                                              J.D. S.B.                                                                               T.B. B.M. Average +/- se                                       __________________________________________________________________________      0   0.00                                                                              0.00                                                                                0.00                                                                               0.00                                                                                0.00                                                                                0.000 +/- 0.000                                      30  0.10                                                                             -0.10                                                                               -0.40                                                                               0.20                                                                                0.00                                                                               -0.040 +/- 0.092                                      60  0.00                                                                             -0.80                                                                               -0.70                                                                              -0.10                                                                               -0.40                                                                               -0.400 +/- 0.141                                      90 -0.20                                                                             -1.10                                                                               -0.70                                                                              -0.40                                                                               -1.10                                                                               -0.700 +/- 0.162                                     120 -0.60                                                                             -1.10                                                                               -1.00                                                                              -0.60                                                                               -1.30                                                                               -0.920 +/- 0.125                                     150 -0.90                                                                             -1.10                                                                               -1.30                                                                              -0.70                                                                               -1.60                                                                               -1.120 +/- 0.140                                     180 -1.10                                                                             -1.15                                                                               -1.20                                                                              -0.90                                                                               -1.70                                                                               -1.210 +/-  0.119                                    __________________________________________________________________________     Treatment-Pure Theobromine (4 mg/kg) and Nutritional Supplement                (Nu. Sp.)                                                                      Subjects                                                                       Time                                                                               M.B.                                                                              J.D. S.B.                                                                               T.B. B.M. Average +/- se                                       __________________________________________________________________________      0   0.00                                                                              0.00                                                                                0.00                                                                               0.00                                                                                0.00                                                                                0.000 +/- 0.000                                      30  0.10                                                                             -0.10                                                                               -0.20                                                                               0.00                                                                                0.10                                                                               -0.020 +/- 0.052                                      60 -0.15                                                                             -0.70                                                                               -0.30                                                                              -0.20                                                                               -0.20                                                                               -0.310 +/- 0.090                                      90 -0.40                                                                             -1.10                                                                               -0.60                                                                              -0.40                                                                               -0.40                                                                               -0.580 +/- 0.121                                     120 -0.50                                                                             -1.10                                                                               -0.90                                                                              -0.50                                                                               -0.60                                                                               -0.720 +/- 0.107                                     150 -0.60                                                                             -1.20                                                                               -0.90                                                                              -0.60                                                                               -0.85                                                                               -0.830 +/- 0.100                                     180 -0.70                                                                             -1.20                                                                               -0.80                                                                              -0.70                                                                               -0.95                                                                               -0.870 +/- 0.084                                     __________________________________________________________________________     Nu. Sp.                                                                        %/w  355 KCal (1480 KJ)                                                        __________________________________________________________________________     16.2 13.0 g Protein (casein and soya protein isolates)                         24.5 19.6 g Fat (corn oil and triglycerides)                                   59.2 47.3 g Carbohydrate (corn syrup solids and sucrose)                               in 235 ml aq. solution                                                 __________________________________________________________________________

                  TABLE 5                                                          ______________________________________                                         Change in rectal temperature (°C.) in male (2) walking                  (5 miles/hour) intermittently (50% of time) at -10° C. for 3            hours                                                                          dressed in shorts.                                                             CHANGE IN RECTAL TEMPERATURE                                                   ______________________________________                                         Treatment-Placebo and Placebo                                                               Subjects                                                          Time           J.D.    S.B.                                                    ______________________________________                                          0              0.00    0.00                                                    30             0.05   -0.40                                                    60            -0.45   -0.70                                                    90            -0.85   -0.70                                                   120            -1.00   -1.00                                                   150            -1.05   -1.10                                                   180            -1.10   -1.20                                                   ______________________________________                                         Treatment-2 mg/kg Theobromine and Nu. Sp.                                                   Subjects                                                          Time           J.D.    S.B.                                                    ______________________________________                                          0              0.00    0.00                                                    30             0.00    0.10                                                    60            -0.40   -0.20                                                    90            -0.85   -0.55                                                   120            -0.90   -0.70                                                   150            -0.90   -0.70                                                   180            -0.90   -0.70                                                   ______________________________________                                         Nu. Sp. = Nutritional Supplement (same as in Table 4)                          %/w        355 KCal (1480 KJ)                                                  ______________________________________                                         16.2       13.0 g Protein                                                      24.5       19.6 g Fat                                                          59.2       47.3 g Carbohydrate                                                               in 235 ml aq. solution                                           ______________________________________                                    

                  TABLE 6                                                          ______________________________________                                         Change in rectal temperature (°C.) in male (1) and female (1)           subjects walking (4-5 miles/hour) intermittently (30% of time) at              -10° C. for 3 hours in shorts (males) or T-shirt and shorts             (females).                                                                     CHANGE IN RECTAL TEMPERATURE                                                   ______________________________________                                         Treatment-Placebo and Placebo                                                               Subjects                                                          Time           A.B.    M.B.                                                    ______________________________________                                          0              0.00    0.00                                                    30            -0.40   -0.15                                                    60            -0.95   -0.50                                                    90            -1.25   -0.80                                                   120            -1.50   -1.05                                                   150            -1.65   -1.20                                                   180            **      -1.40                                                   ______________________________________                                         Treatment-CHOP 2 mg/kg Theobromine via Cocoa.                                               Subjects                                                          Time           A.B.    M.B.                                                    ______________________________________                                          0              0.00    0.00                                                    30            -0.50    0.00                                                    60            -0.65   -0.30                                                    90            -0.75   -0.50                                                   120            -0.85   -0.80                                                   150            -0.95   -0.90                                                   180            -0.90   -1.00                                                   ______________________________________                                         CHOP = Carbohydrate Protein Supplement                                         %/w        250 KCal (1042 KJ)                                                  ______________________________________                                         46.2       30.0 g Casein (calcium caseinate)                                    5.2        3.4 g Glucose                                                      15.5       10.1 g Sucrose                                                      33.1       21.5 g Corn Starch                                                              9.0 g Cocoa (containing 1.5%/w Theobromine)                                      in 235 ml aq. solution.                                          ______________________________________                                          **Individual removed from cold due to reaching maximum allowable decrease      in body temperature.                                                      

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. A method of improving the cold tolerance of animals and humans which comprises administering to an animal or human in need thereof an orally ingestible composition consisting essentially of an adenosine receptor antagonist selected from the group of caffeine, theobromine, 8-phenyltheophylline, 8-cyclopentyltheophylline, 8-(4-(2-aminoethyl)amino carboxymethyloxyphenyl)-1,3-dipropylxanthine, 8-(amino-4-chlorophenyl)-1,3-dipropyl xanthine, and 8-(p-sulfophenyl)-1,3-dipropyl xanthine, alone or mixed with two or more thereof, or in combination with theophylline or aminophylline or both, and a nutritional supplement mixture of 47 to 66% by weight of carbohydrate, 15-50% by weight of protein and 0 to 25% by weight of fat, said composition administered in an amount sufficient to improve the cold tolerance of said animal or human.
 2. The method according to claim 1, wherein said adenosine receptor antagonist is theobromine.
 3. The method according to claim 1, wherein said adenosine receptor antagonist is caffeine.
 4. The method according to claim 1, wherein said adenosine receptor antagonist is 8-phenyltheophylline.
 5. The method according to claim 1, wherein said adenosine receptor antagonist is 8-cyclopentyltheophylline.
 6. The method according to claim 1, wherein said adenosine receptor antagonist is 8-(4-(2-aminoethyl)aminocarboxymethyloxyphenyl)-1,3-dipropylxanthine.
 7. The method according to claim 1, wherein said adenosine receptor antagonist is 8-(amino-4-chlorophenyl)-1,3-dipropylxanthine.
 8. The method according to claim 1, wherein said adenosine receptor antagonist is 8-(p-sulfophenyl)-1,3-dipropylxanthine.
 9. The method according to claim 1, wherein said adenosine receptor antagonist is a mixture of 8-phenyltheophylline and aminophylline.
 10. The method according to claim 1, wherein the carbohydrate in the nutritional supplement mixture contains glucose, sucrose and starch in a weight ratio of about 1:3:6 to about 1:10:10.
 11. The method according to claim 1, wherein the carbohydrate is a sugar.
 12. The method according to claim 11, wherein the sugar is selected from sucrose and glucose.
 13. The method according to claim 1, wherein the carbohydrate is starch.
 14. The method according to claim 1, wherein the carbohydrate is a mixture of a sugar and starch.
 15. The method according to claim 14, wherein the carbohydrate is a mixture of glucose, sucrose and starch.
 16. The method according to claim 15, wherein the weight ratio of glucose to sucrose to starch is about 1:3:6.4, wherein 1=0.26 g.
 17. The method according to claim 15, wherein the weight ratio of glucose to sucrose to starch is about 1:5:10.6, wherein 1=0.26 g.
 18. The method according to claim 14, wherein the adenosine receptor antagonist is theobromine.
 19. The method according to claim 15, wherein the adenosine receptor antagonist is theobromine.
 20. The method according to claim 16, wherein the adenosine receptor antagonist is theobromine.
 21. The method according to claim 17, wherein the adenosine receptor antagonist is theobromine.
 22. The method according to claim 1, wherein the carbohydrate is a sugar.
 23. The method according to claim 1, wherein the carbohydrate is a mixture of a sugar and starch.
 24. The method according to claim 23, wherein the carbohydrate is a mixture of glucose, sucrose and starch.
 25. The method according to claim 24, wherein the adenosine receptor antagonist is theobromine.
 26. The method according to claim 25, wherein the protein is egg albumin and wherein the fat is corn oil.
 27. The method according to claim 26, wherein the mixture comprises glucose:sucrose:starch:egg albumin:corn oil in a weight ratio of about 1:3:6.4:5:0.33.
 28. The method according to claim 1, wherein the adenosine receptor antagonist is theobromine in an amount of about 2 to 4 mg/kg of body weight.
 29. The method according to claim 28, wherein the theobromine is in the form of cocoa powder containing 1-2% by weight of theobromine in said powder.
 30. The method according to claim 1, wherein the nutritional supplement is a mixture of 50-60% by weight of carbohydrate, 15-50% by weight of protein and 0-25% by weight of fat.
 31. The method according to claim 30, wherein the carbohydrate is a mixture of sucrose and corn syrup solids.
 32. The method according to claim 31, wherein the protein is a mixture of casein and soya protein isolates.
 33. The method according to claim 32, wherein the fat is oil.
 34. The method according to claim 33, wherein the mixture of carbohydrate, fat and protein comprises, about 59.2% by weight of corn syrup solids and sucrose, about 24.5% by weight of corn oil, and about 16.2% by weight of casein and soya protein isolates.
 35. The method according to claim 30, wherein the carbohydrate is a mixture of glucose, sucrose and corn starch.
 36. The method according to claim 35, wherein the protein is casein.
 37. The method according to claim 36, wherein the amount of theobromine is about 2 mg/kg of body weight.
 38. The method according to claim 37, wherein the nutritional supplement comprises about 53% by weight of carbohydrate and about 46.2% by weight of protein. 